The present invention relates to a helical locking mechanism for weapons with sliding chambers. In weapons of this type, the firing chamber is separate from the gun tube or barrel, and slides longitudinally within the weapon frame or receiver. As a round of ammunition is fed into the receiver, the chamber moves forward, encapsulating the round. The chamber must be locked in this position before the weapon is fired. This is to prevent recoil forces from damaging other weapon components and to prevent the loss of propellent gases. Obviously if propellent gases were allowed to escape from the chamber during firing, the velocity of the fired projectile would be greatly reduced. This is especially true when using telescoped or caseless ammunition. In telescoped rounds the projectile is surrounded by propellent and encased in a metal casing. Caseless ammunition is of similar construction, but without the metal casing. This type of round is entirely dependent on chamber sealing to contain the propellent gases, since there is no cartridge casing. These rounds are generally the type of ammunition associated with sliding chamber weapons. Therefore chamber sealing is critical.
Normally, conventional locking mechanisms do not provide means to tightly seal the chamber against the breech end of the gun tube, but simply retain the chamber once it is positioned in battery position. Great precision is then required in manufacturing the chamber and related components to achieve the proper fit and sealing required. This increases the cost of weapon components without completely eliminating the problem of gas leakage from the chamber. Even in the most carefully machined components certain clearances are necessary for proper operation. For example, lug type locking mechanisms utilize one or more lugs which are engageable with recesses in the receiver. The recess, to receive the locking lug, must be slightly larger than the lug itself to allow smooth operation of the mechanism during locking and unlocking. This built-in clearance allows some minute chamber movement while in the locked position. This is a compromise situation which is generally accepted in current gun designs. Also minute changes in chamber dimensions occur after a few rounds are fired. This is due to thermal expansion; i.e., the chamber expands due to the heat generated from firing previous rounds. This further aggravates the problem of chamber sealing.